1. FIELD OF THE INVENTION
This invention relates to the field of mechanical seals, and more particularly to a mechanical end face seal having a novel construction for sealing a rotating shaft against fluid leakage.
2. BRIEF DESCRIPTION OF THE PRIOR ART
Establishing a seal between a rotating shaft and the wall of a container while preventing the fluid in the container from escaping can be quite difficult. The shaft must be sealed in both its static and dynamic condition with the same sealing device.
Mechanical end face seals are commonly used in such applications. A mechanical end face seal has been defined as a machine element that prevents fluid from escaping a container at a rotating shaft extending through its housing utilizing axial force to keep the end faces of the primary sealing elements, which are 90.degree. to the shaft axis, in contact.
Primary sealing elements in common mechanical end face seals consist of a seat inserted into the housing wall and a washer riding against the seat. The primary dynamic seal takes place at the contacting end faces of the two elements. To compensate for wear between the two sliding faces and maintain face contact, the washer is held against the seat by means of one or more springs. The springs are contained in a retainer which is attached to the shaft by set screws or other means. The retainer may have drive dents that engage in mating grooves of the washer, and as the shaft rotates, the entire seal head (retainer, springs, and washer) rotates with it.
Many material combinations have been used for the primary sealing element faces such as; carbon running against cast iron, Ni-resist, ceramic, Stellite, or tungsten carbide.
Secondary sealing elements are provided since the primary sealing elements are separate pieces. O-rings are widely used for this purpose. An O-ring is commonly placed between the outside diameter of the seat and the inside diameter of the wall housing to provide a static seal. Placing another O-ring between the outside diameter of the shaft and the inside diameter of the washer provides a semi-static seal. Since the washer moves slightly forward as the washer face wears down, it is not a true static seal.
Prior art seals of this type are shown in Bulletin No. S-2021, "End Face Shaft Seals" by Crane Packing Company, 6400 Oakton St., Morton Grove, Ill. 60053.
Failure of mechanical end face seals is often due to loss of the secondary O-ring seal between the outside diameter of the shaft and the inside diameter of the washer. Major causes of the loss are vibration and shaft galling due to abrasive particles in the fluid being handled packing in the annular opening between the shaft and the washer. Since these seals often compensate for vibration due to shaft misalignment and are used in applications involving abrasive and corrosive material handling, replacement and costly down time is a common occurrence. It is not unusual for these seals to require replacement as often as every month.
There has been a need for a mechanical end face seal having improved secondary sealing characteristics that will prolong the seal life of the assembly and provide resistance to shaft galling.